where $\sigma_1^{dev}$ is the maximum deviatoric principal stress and $p$ is the pressure.
With $\beta_s = 0$, $\bar{\sigma}_1$ equals the maximum principal stress.
Note that the damage only grows if $\bar{\sigma}_1 \geq \sigma_s.$

Crack propagation is controlled by a stress intensity criterion (if having node splitting activated). The stress intensity $K_I$ is estimated
for the integration points surrounding the crack tip. The crack will propagate if $K_I > K_c$ (Modus I crack).